On the Relation between Carbide Density and Grain Boundary Character in Tempered Martensite Ferritic Steels

摘要

In the present study we investigate the microstructure of tempered martensite ferritic steels. It is well known that inside former austenite grains and inside packets of former martensite laths ultrafine micro grains (average size near: 1 fjm) govern the strength of this material class. Micro grain boundaries are decorated by carbides (average size after creep near: 0.05 mu m). However, in transmission electron micrographs it is commonly found that there are micro grain boundaries with a high carbide density while there are others where no carbides can be detected. In the present study we make an attempt to decide whether the crystallographic character of micro grain boundaries can be related to the number density of carbides at the boundaries. Kikuchi line diffraction patterns were used to determine the misorientation angle between two adjacent micro grains; we select only micro grain boundaries which represent <110> - and <100> - twist boundaries. A quantitative microstructural analysis was performed to determine the density of carbides on boundaries. Our results are discussed on the basis of general tendencies which were reported for grain boundaries in the literature.